The present invention relates to an apparatus and method for introducing materials into an ore processing furnace for improved reduction of iron oxide. More particularly, this invention relates to the composition of materials introduced into a furnace for increasing/controlling the melting point of hearth compounds and for coating the hearth surface to improve the reduction and metallization of iron oxide.
Steel, by definition, is a combination of iron with a small amount of carbon and other materials. Iron does not occur in nature in its useful metallic form. Metallic iron, from which steel is derived, much be extracted from iron ore. Generally, the ratio of metallic iron to total iron is termed metallization.
All steelmaking processes require the input of iron bearing materials as process feedstocks. For making steel in a basic oxygen furnace, the iron bearing feed materials are usually blast furnace hot metal and steel scrap. A broadly used iron source is a product known as Direct Reduced Iron (xe2x80x9cDRIxe2x80x9d) which is produced by the solid state reduction of iron ore to highly metallized iron without the formation of liquid iron.
A common problem with current methods for producing metallized iron product is the loss of purified metallized iron within the furnace at elevated temperatures. Additionally, the current methods for obtaining increased volumes and a higher quality of metallized iron product from rotary hearth furnaces involve significant expenditures, increased processing time, and/or excessive furnace temperatures.
In 1987, Midrex received U.S. Pat. No. 4,701,214, that taught reduction in a rotary hearth furnace and a method of operation in which finely divided iron oxide and carbonaceous material is devolatized, with a substantial portion being reacted, forming hot, highly reduced iron containing some carbon for feed material for additional smelting and refining.
U.S. Pat. No. 5,730,775 teaches a method and apparatus for producing direct reduced iron from dry iron oxide and carbon compacts that are placed no more than two layers deep onto a rotary hearth, and are metallized by heating the compacts to temperatures of approximately 1316xc2x0 to 1427xc2x0 C., for a short time period. For a general understanding of the recent art, U.S. Pat. No. 5,730,775 is incorporated herein by reference.
Because of the problems of the prior art, a need therefore exists for an apparatus and method of operation for efficiently producing increased volumes and a higher quality of metallized iron product from rotary hearth furnaces without significant increases in cost, processing time, or excessive furnace temperatures.
While there are numerous methods and means for producing increased volumes and higher quality metallized iron product from rotary hearth furnaces, none are known to have a similar structure to, or to function in the manner of the present invention.
Direct reduction of iron oxide in furnaces utilizing the invented apparatus and method improves the utilization of a hearth furnace by providing a moving hearth with a refractory base layer thereon and a vitreous hearth layer on the refractory base layer. The vitreous hearth layer is composed of conditioning materials that increase the melting point of the vitreous layer onto which iron oxide pellets are placed. The conditioning materials may be provided as multiple layers on the base layer, with an upper layer or coating of non-wetting graphite compounds. Multiple vitreous hearth layers may contain components that increase the melting point of the vitreous hearth layers, and may include upper layers of carbon or carbon compounds that reduce the adherence of liquified iron and carbon to the vitreous hearth layer, thereby improving the efficiency of the direct reduction of iron oxide feed material to metallized iron discharged from the furnace.
The present invention is an improved hearth apparatus and a method of operation that provides conditioning materials that may include compounds such as magnesium oxide compounds, silicon oxide compounds, aluminum oxide compounds, iron oxide compounds, and a carbon compound source that are introduced in layers onto a refractory base layer, and are melted to form vitreous hearth layers. An additional upper coating layer of carbonaceous materials is added and iron oxide pellets are placed for reduction. The invention provides for the production of increased volumes of product and a higher quality carbon-containing metallized iron product than previously available. The iron product is separated from slag in the furnace without significant increases in costs, processing time, or excessive furnace temperatures over prior known processes.
The principal object of the present invention is to provide a method of achieving efficient reduction of iron oxide to metallized iron at elevated temperatures in a processing and reducing furnace having a hearth surface, preferably a moving hearth.
It is also an object of this invention to provide a method of achieving efficient reduction of iron oxide at elevated temperatures in a processing and reducing furnace which allows ease of removal of metallized iron oxide from the hearth surface.
Another object of the invention is to provide an improved furnace apparatus for introducing refractory surface conditioning material onto the base layer of the furnace.
Another object of the invention is to provide an improved hearth furnace method of operation which provides hearth conditioning materials forming solidified vitreous hearth layers at high temperatures utilized for producing metallizing iron material.
An additional object of the invention is to provide a method of operation of a rotary hearth furnace including applying conditioning materials on a refractory surface, with placement of coating layers providing ease of removal of metallized iron product from the vitrified hearth surface.
The objects of the invention are met by a method for producing direct reduced, purified, metallized iron at elevated temperatures within a furnace, including the step of providing a furnace having a refractory layer, introducing conditioning materials on the refractory layer, heating the conditioning materials to form a vitreous layer on the refractory layer, and placing a coating layer on the vitreous layer. Iron oxide materials are placed on the coating layer, exposed to elevated temperatures, and reduced to purified metallized iron nuggets, which are discharged from the furnace.
The objects of the invention are also met by an apparatus for producing direct reduced metallized iron at elevated temperatures within a furnace, the furnace having a refractory layer with a means for introducing conditioning materials on the refractory layer. The conditioning materials include carbonaceous materials including a mixture of magnesium oxide, silicon oxide, aluminum oxide compounds, iron oxide compounds and a carbon source, placed in multiple layers on the refractory layer. The conditioning materials are heated to form vitreous hearth layers. A carbon coating layer is applied to the vitreous hearth layers, and iron oxide feed materials are placed on the coating layer. The iron oxide materials are heated by a radiant heat source within the furnace to form purified metallized iron nuggets, which are discharged from the furnace.